Optical router with nearly ideal performance and increased number of channels

Abstract

An optimized planar optical router consisting of two stages performing stationary imaging between an input waveguide and a set of output waveguides has advantages of reduced size, larger number of channels and minimal loss variation in each passband. The new router is an optimized M×N imaging arrangement including two waveguide gratings and n waveguide lenses connected between the principal zones of the two gratings. The largest values of N are realized by using a combination of two techniques that increase N without increasing the size of the two gratings. One technique increases N for a given number n of lenses and, the other, increases n. In one embodiment, each lens produces a periodic sequence of passbands, all transmitted from a particular input waveguide to the same output waveguide, whereas, in a second embodiment, the above passbands are transmitted to different output waveguides. In both cases, the loss caused by secondary images is substantially reduced by including secondary lenses.

1. A planar optical router comprising two stages of imaging and a number n of principal lenses connected between the principal zones of the two stages;
 the number n is greater than one; 
 each stage consists of a waveguide grating performing imaging between the two focal curves of the grating; 
 the router includes at least one input waveguide and N output waveguides; wherein: 
 the input and output stages have substantially opposite dispersions, so that the router frequency response to an input signal substantially produces a set of N maximally flat passbands; 
 said N passbands are respectively transmitted to the N output waveguides; and 
 the ratio between the free-spectral ranges of the two stages is properly chosen so that said passbands comprise several sets produced by different orders of the input stage. 
 
     
     
       2. The planar optical router as recited in  claim 1  wherein:
 the number N is greater than n; and 
 at least two of the principal lenses are combined with secondary lenses located outside the principal zones of the two stages. 
 
     
     
       3. The planar optical router as recited in  claim 1  wherein:
 the router includes outside the principal zones two sets of secondary lenses; 
 the principal set is located between the two secondary sets; 
 the output apertures of the principal lenses have substantially constant width W and substantially constant gap width S between adjacent apertures; 
 each gap width S 0  between adjacent lenses belonging to different sets is substantially equal to S; 
 W is an integer multiple of S; and 
 the diffraction orders Q and Q′ of the first and second stage substantially satisfy the condition 
 
       
         
           
             
               
                 
                   
                     Q 
                     ′ 
                   
                   Q 
                 
                 = 
                 
                   1 
                   - 
                   
                     1 
                     r 
                   
                 
               
               , 
             
           
         
         where r≅m+1 and m=W/S. 
       
     
     
       4. The planar optical router as recited in  claim 1  wherein:
 the number of input waveguides is equal to the number N of output waveguides; 
 the number n of principal lenses is equal to N; 
 the router performs a total of N 2  connections; and 
 at least two of the principal lenses are combined with secondary lenses located outside the principal zones of the two stages. 
 
     
     
       5. The planar optical router as recited in  claim 1  wherein:
 the lenses are segmented to minimize the total length required between the two stages. 
 
     
     
       6. A planar optical router comprising two stages of imaging and a number n of principal lenses connected between the principal zones of the two stages;
 the number n is greater than one; 
 each stage consists of a waveguide grating performing imaging between the two focal curves of the grating; wherein: 
 the router includes a number M of input waveguides and a number N of output waveguides; 
 both M and N are greater than one; 
 the two stages are characterized by substantially equal free-spectral ranges; 
 the router performs a total of MN connections; and 
 each connection includes at least two widely spaced passbands whose frequency spacing is substantially equal to the free-spectral ranges of the two stages, and at least two of the principal lenses are combined with secondary lenses located outside the principal zones of the two stages, and at least two of the principal lenses are combined with secondary lenses located outside the principal zones of the two stages.